Don Butler Custom Built Gt5A-ES SkyHawk Minarelli 70cc engine with OCDT

HuRah!  The next 2 customers will receive an OCDT included with this Don Butler Custom Gt5A-ES 70cc Minarelli Cylinder modified engine.   

Except for the 4 we have left we won't have any more CCW OCDT for handheld drill starting until July 2023.  Christmas is coming so get mama to order this engine early!   The engine price will come down when the last OCDT are shipped out. 

Our new design OCDT has a 3/8" socket drive to attach a M6 hex 3/8" socket and a M10 hex shaft to attach to a 1/2" drill or use a M10 1/2" socket for use with a modified 1/2" impact drive tool.

This engine consists of a Gt5A-ES SkyHwk bottom half and a Minarelli 70cc vertical top end.   Everything hand fitted to perfection. 

Introducing you to the world-famous old codger "Roy Don Butler" who owns and operates Don's Speed Shop dba: Pedals to Power in Chickasha OK.   

Don is a full-time engine builder that takes our 66cc Gt5A-ES engine to the next plateau of performance and goes totally beyond expectations.  

Here's what he does.

  • Completely disassembles a stock SkyHawk Gt5A-ES engine.

  • Drills more holes in the crank fly wheels to match the counterbalance weight of the piston, pin and connecting rod resulting in less engine vibration. 

  • Does a custom porting job on the cylinder 

  • Installs a windowed 47mm piston and new bearings.     

  • Installs a CNC cut spacer plate under the cylinder and makes sure the piston squish to be no more than 0.75 to 0.8mm. 

  • Installs a DLH SAF Clutch by removing the stock SkyHawk clutch shaft spring and then installs a 3 spring heavy duty clutch plate which prevents a slipping clutch due to higher achieved torque. 

  • Installs a Flat Reed Valve assembly for piston port induction.  

  • Installs a high-quality Knockoff Mukuni VM22mm carburetor which is much larger and more expensive than the NT 14.95mm dia. slide valve found with stock China doll 66cc engines.  

  • Installs a high compression CNC head with a thin copper head gasket.   

  • Installs larger M8 mounting studs on rear of the engine for more secure mounting to the bike's seat tube. 

  • Bench runs a brief live test with a dedicated carb to confirm all is ready to go "Hot" for lock and load!


  • Don includes an assortment of jets so the end user can tune as required for the conditions in their locality.   

  • This engine is not a fuel saving get around town on a dime engine.   It's made to turn enthusiasm into fear!    

  • Don says 40 to 50 mph has been documented with this engine properly tuned with expansion chamber exhaust and ran with the right ratio rear sprocket on flat land when ridden by a well-trained Chimpanzee.  Ha-ha! Just kidding about the Chimp rider!

  • The SkyHawk OCDT cordless electric drill start feature is greatly appreciated when starting this hopped-up engine without having to pedal start or flip start via the rear wheel.   

  • OCDT ( Over-Running Clutch Drive Tool ) is included for the next 2 buyers only.   Why ? cause that's all we have left until the next shipment arrives next year. 

  • When you order this engine, it is dropped shipped direct from Don's Speed Shop to your doorstep.   

  • We can provide you with the contact email and phone # so you can deal directly with Don on any issues of importance or warranty.